Grease composition for constant velocity joint and constant velocity joint

ABSTRACT

The invention provides a grease composition for constant velocity joint containing the components (a) to (g) below and a constant velocity joint containing said composition. (a) a diurea thickening agent having the following formula (1):
 
R 1 NH—CO—NH—C 6 H 4 - p -CH 2 —C 6 H 4 - p -NH—CO—NHR 2   (1)
 
wherein R 1  and R 2  may be the same or different and represent C 8 -C 20  alkyl groups, (b) an ester synthetic oil, (c) a mineral oil and/or a synthetic hydrocarbon oil, (d) a molybdenum dialkyldithiocarbamate, (e) molybdenum disulfide, (f) a polytetrafluoroethylene, and (g) a zinc dithiophosphate compound. The grease composition of the invention reduces variations in rotational resistance of the constant velocity joint at a low temperature.

This application is a continuation of U.S. Pat. No. 8,377,858, filed May21, 2008, and assigned U.S. application Ser. No. 12/124,916, and whichis a continuation of International Application No. PCT/JP2006/323289,filed 22 Nov. 2006, which claims priority to Japan Application No.2005-337550, filed 22 Nov. 2005, the entire contents of each of whichare hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to a grease composition for a constant velocityjoint which can reduce variation in rotational resistance, at a lowtemperature, of the constant velocity joint and a constant velocityjoint containing said grease composition. More specifically, thisinvention relates to a grease composition for a constant velocity jointwhich is suitable to reduce variation in rotational resistance, at a lowtemperature, of a fixed type constant velocity joint or a sliding typeconstant velocity joint used for automobile driving shafts, and aconstant velocity joint containing the same.

BACKGROUND OF THE INVENTION

In the field of automobile industry, FF-car production has recently beenincreasing for the purpose of reducing weight and expanding livingspace. 4WD car production is also growing due to their functionality.These FF and 4WD cars realize a power transmission and steering by thefront wheels, and therefore, it is necessary to secure a smooth powertransmission, even when the steering wheel is fully turned, and theconstant velocity joint is inevitable as a part to transmit a rotationalmovement at a constant velocity in response to the changes in crossingangles between the crossing two axes.

Because performance of cars has recently been improved further and theproduction of high-power cars is increasing, constant velocity jointsare exposed to greater stresses and severer lubrication condition.

Meanwhile, there is a tendency that an improvement of riding comfort ina car is also required at a higher level. The improvement of the ridingcomfort is demanded in any climate regions, for example, from extremehot regions to extreme cold regions.

In extreme cold regions, the car may be started at an extreme lowtemperature. In such a condition, the rotational resistance may varyupon rotating due to the difference in frictional resistances amongparts composing the constant velocity joint. Variation in rotationalresistance may generate stick-slip sounds which may then lead todeteriorate the riding comfort.

There have been proposed grease compositions for constant velocityjoints wherein a mineral oil is used as a base oil and a molybdenumcompound is used as an additive (see e.g. Patent Documents 1 and 2).However, these grease compositions for constant velocity joints areincapable of sufficiently reducing variation in rotational resistancewhen different factors become combined at an extreme low temperature,therefore an improvement for more stable performance is required.

-   Patent document 1: JP-A-H10-273692-   Patent document 2: JP-A-2003-165988

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

An object of the present invention is to provide a grease compositionfor a constant velocity joint which can reduce variation in rotationalresistance, at a low temperature, of the constant velocity joint.

Another object of the invention is to provide a constant velocity jointwhich contains the aforementioned grease composition for the constantvelocity joint.

Means to Solve the Problem

In order to achieve the aforementioned object, the present inventorshave extensively studied to achieve the above object and found that thegrease composition which contains specific components can reducevariation in rotational resistance, at a low temperature, of theconstant velocity joint. Based on this finding, they have completed thepresent invention.

Accordingly, the invention provides a grease composition for a constantvelocity joint shown below and a constant velocity joint which containsthe same.

1. A grease composition for a constant velocity joint, said compositioncomprising the following components (a) to (g):

(a) a diurea thickening agent having the following formula (1):R¹NH—CO—NH—C₆H₄-p-CH₂—C₆H₄-p-NH—CO—NHR²  (1)wherein R¹ and R² may be the same or different and represent C₈-C₂₀alkyl groups,(b) a synthetic ester oil,(c) a mineral oil and/or a synthetic hydrocarbon oil,(d) a molybdenum dialkyldithiocarbamate,(e) molybdenum disulfide,(f) a polytetrafluoroethylene, and(g) a zinc dithiophosphate compound.2. The grease composition for a constant velocity joint according to theabove item 1, wherein the content of the component (a) is 1-20% by mass,the content of the component (b) is 5-40% by mass, the content of thecomponent (c) is 40-80% by mass, the content of component (d) is 0.1-10%by mass, the content of the component (e) is 0.1-10% by mass, thecontent of the component (f) is 0.1-10% by mass and the content of thecomponent (g) is 0.1-10% by mass based on the total mass of thecomposition.3. The grease composition for a constant velocity joint according to theabove item 1 or 2, wherein the component (b) is a synthetic ester oilobtained from a polyol having three or more hydroxyl groups and acarboxylic acid.4. The grease composition for a constant velocity joint according to anyone of the above items 1 to 3, wherein a flow point of the syntheticester oil, the component (b), is not higher than −40° C.5. The grease composition for a constant velocity joint according to anyone of the above items 1 to 4, wherein a kinetic viscosity of thesynthetic ester oil, the component (b), is not less than 40 mm²/S at 40°C.6. The grease composition for a constant velocity joint according to anyone of the above items 1 to 5, wherein the torque transmission part ofthe constant velocity joint is in the shape of a ball.7. The grease composition for a constant velocity joint according to anyone of the above items 1 to 6, wherein said constant velocity joint is afixed type constant velocity joint.8. The grease composition for a constant velocity joint according to anyone of the above items 1 to 6, wherein said constant velocity joint is asliding type constant velocity joint.9. A constant velocity joint which comprises the grease composition fora constant velocity joint according to any one of the above items 1 to8.

Effects of the Invention

The grease composition of the invention for a constant velocity joint ishighly useful for reducing variation in rotational resistance, at a lowtemperature, of the constant velocity joint, such as a fixed typeconstant velocity joint and a sliding type constant velocity joint,which are used for the automobile driving shaft. The invention alsoprovides a constant velocity joint which contains the grease compositionfor a constant velocity joint having such excellent properties.

The application condition of constant velocity joints has been expandingin association with recent economic growth, and as a result, therequirements for the performance thereof have also become diversified,enhancing the importance of smooth working of the constant velocity inextreme cold regions.

However, a grease composition for a constant velocity joint which canreduce variation in rotational resistance of the constant velocity jointsufficiently at a low temperature has not yet become available. Undersuch a situation, the grease composition of the invention for a constantvelocity joint, which can reduce variation in rotational resistance ofthe constant velocity joint at a low temperature may be considered as anextremely useful invention.

The invention is based on the finding that the grease composition for aconstant velocity joint which contains specific components can achievethe aforementioned purposes. For a reason the grease composition of theinvention for a constant velocity joint has an excellent activity toreduce variation in rotational resistance at a low temperature, it maybe possible that fluidity, viscosity and lubricity, etc. becomeoptimized at a low temperature by using certain urea compounds as athickening agent and certain synthetic oils as a base oil and by addingspecific molybdenum compounds, zinc dithiophosphate compounds andpolytetrafluoroethylenes as additives, thereby reducing variation inrotational resistance.

BEST MODES FOR CARRYING OUT THE INVENTION

The invention will be explained in more detail as follows.

The grease composition of the invention for a constant velocity joint isa grease like composition which can be used for a constant velocityjoint, wherein the constant velocity joint is a part which transmits arotational movement at a constant velocity in response to changes incrossing angle between the crossing two axes. Further, the grease meansa solid or semi-solid substance prepared by dispersing thickening agentsinto a base oil.

The grease composition of the invention for a constant velocity joint ischaracterized by comprising the components (a) to (g) as essentialcomponents. Each component will be explained in more detail below.

Firstly, the diurea thickening agent, the component (a) of the inventionhas the following formula (1):R¹NH—CO—NH—C₆H₄-p-CH₂—C₆H₄-p-NH—CO—NHR²  (1)wherein R¹ and R² may be same or different and represent C₈-C₂₀ alkylgroups.

The diurea thickening agent, component (a), can be obtained, forexample, by reacting certain diisocyanates with certain monoamines. Theisocyanate is more specifically, diphenylmethane-4, 4′-diisocyanate.

Monoamines include aliphatic amines, aromatic amines, alicyclic aminesor mixture thereof. Specific examples of the aliphatic amines includeoctylamine, dodecylamine, hexadecylamine, octadecylamine and oleylamine.Specific examples of the aromatic amines include aniline andp-toluidine. Specific examples of the alicyclic amines includecyclohexylamine. Among the aforementioned monoamines, diurea thickeningagents, which can be prepared with octylamine, dodecylamine,hexadecylamine, octadeclyamine or a mixture thereof, are preferred.

The content of the diurea thickening agent, component (a), based on thetotal mass of the composition depends on the types of the agents. Theconsistency (worked penetration) of the grease of the invention ispreferably within a range of 250-350, and accordingly, the content ofthe diurea thickening agent, component (a), is preferably in an amountrequired to display such consistency. The content of the diureathickening agent, component (a), can be, for example, 1-20% by mass,preferably 2-20% by mass based on the total mass of the composition butnot limited to these.

The synthetic ester oil, component (b) of the invention is representedby trimellitic acid esters and polyol esters, but most preferablysynthetic ester oil which can be obtained from polyols having three ormore hydroxyl groups and carbonic acids, and has a flow point of nothigher than −40° C. and a kinetic viscosity of not less than 40 mm²/S at40° C. The content of the synthetic ester oil, component (b), can be forexample, 5-40% by mass, preferably 10-40% by mass, based on the totalmass of the composition, but not limited to these.

A mineral oil and/or a synthetic hydrocarbon oil, component (c) of theinvention can be used as a base oil, either alone or in combination. Thecontent of the mineral oil and/or synthetic hydrocarbon oil, component(c), can be the balance, i.e. the balancing amount against all addedcomponents including an optional component(s), based on the total massof the composition.

Preferably, a molybdenum dialkyldithiocarbamate, component (d) of theinvention has the formula (2) below.(R³R⁴N—CS—S)₂—Mo₂O_(m)S_(n)  (2)wherein R³ and R⁴ independently represent, for example, C₁-C₂₄ alkylgroups, preferably C₂-C₁₈ alkyl groups, m is 0-3, n is 1-4 and m+n=4.The content of the molybdenum dialkyldithiocarbamate, the component (d),is preferably 0.1-10% by mass, more preferably 0.5-5% by mass, based onthe total mass of the composition.

Molybdenum disulfide, the component (e) of the invention is widely usedas a solid lubricant for constant velocity joints. As for the mechanismof lubrication, molybdenum disulfide is known to have a layer-latticestructure which can easily be sheared into thin layer structures bysliding, thereby reducing friction resistance. It also displays aneffect to prevent seizing of constant velocity joints.

The content of molybdenum disulfide, the component (e), is preferably0.1-10% by mass, more preferably 0.5-5% by mass, based on the total massof the composition. The amount to be added is preferably in the rangewhere the vibration properties or the friction coefficients of constantvelocity joints are not adversely affected.

A polytetrafluoroethylene, the component (f) of the invention, is onegenerally used in the fields of rubber, paint, ink and lubricant otherthan grease and have the molecular weight between several thousands andseveral hundred thousands. Because the cohesive energy ofpolytetrafluoroethylene is lower than those of other polymericcompounds, and the critical surface tension is extremely small, it isconsidered that a shear stress due to sliding makes thepolytetrafluoroethylene particles present in sliding area into tinyflakes which easily spread on the object materials, thereby providingexcellent lubrication properties. The content of thepolytetrafluoroethylene, the component (f), is preferably 0.1-10% bymass, more preferably 0.5-5% by mass, based on the total mass of thecomposition.

A zinc dithiophosphate compound, the component (g) of the invention is azinc dialkyldithiophosphate, a zinc diaryldithiophosphate and the like.The content of the zinc dithiophosphate compound, the component (g), ispreferably 0.1-10% by mass, more preferably 0.5-5% by mass, based on thetotal mass of the composition.

In addition to the above components, the grease composition of theinvention may contain other additives such as extreme-pressureadditives, anti-oxidants, rust preventing agents, anti-corrosive agentsand the like, which are conventionally used for the grease composition.

The constant velocity joint of the invention, wherein the torquetransmission part of the constant velocity joint is sphere, includes afixed type constant velocity joint such as Rzeppa and Birfield types ora sliding type conventional velocity joint such as double offset orcross group types. They utilize balls as torque transmission parts,which are placed on the tracks formed on the outer and inner races, andhave a structure to be incorporated through the cage.

A constant velocity joint wherein the constant velocity joint of theinvention is a fixed type constant velocity joint includes theaforementioned fixed type constant velocity joint such as Rzeppa andBirfield types, and can form a large operation angle not less than 45°.

A constant velocity joint wherein the constant velocity joint of theinvention is a sliding type constant velocity joint includes theaforementioned sliding type constant velocity joint such as doubleoffset or cross group types, and cannot take form an operation angle aslarge as in the case of the fixed type constant velocity joint, but canslide in the direction of the axis.

The invention will now be described with reference to examples. Itshould be noted, however, that the examples do not intend to limit thescope of the invention. It should also be noted that reasonablevariations can be made within the spirit of the invention, however, suchvariations are still included within the scope of the invention.

EXAMPLES 1-4, COMPARATIVE EXAMPLES 1-4 Preparation of Grease Composition

In 3,700 g of the mineral oil (c) (kinetic viscosity of 11 mm²/s at 100°C.), 250 g (1 mole) of diphenylmethane-4,4′-diisocyanate, 129 g (1 mole)of octylamine and 270 g (1 mole) of octadecylamine were reacted, and theresulting diurea compound (a) was dispersed evenly to obtain a basegrease. Base oils and additives were added to the above base grease toprepare the composition as shown in Table 1 or 2. The resultingcomposition was kneaded with a triple rolling mill and the workedpenetration was adjusted to 300 according to JIS 2220.

The composition of the tested products and the results of the variationsin the rotational torque at −40° C. are shown in Table 1 for Examplesand in Table 2 for Comparative Examples.

TABLE 1 Mass % Examples 1 2 3 4 Thickening (a) Diurea compound   8.0agent Base oil (b) Synthetic ester oil *¹ 17.0  8.5 17.2  34.0  (mixing(20) (10) (20) (40) ratio %) (c) -1 Mineral oil 51.0  51.0  51.6  51.0 (60) (60) (60) (60) (c) -2 Synthetic 17.0  25.5  17.2  hydrocarbon oil*² (20) (30) (20) Additives (d) Molybdenum 2.0 2.0 2.0 2.0dialkyldithiocarbamate *³ (e) Molybdenum disulfide *⁴ 3.0 3.0 1.0 3.0(f) Polytetrafluoroethylene *⁵ 1.0 1.0 2.0 1.0 (g) Zinc dithiophosphate1.0 1.0 1.0 1.0 compound *⁶ Worked penetration 300 Evaluation ofvariation in rotating ∘ ∘ ∘ ∘ torque at −40° C.

TABLE 2 Mass % Comparative Examples 1 2 3 4 Thickening (a) Diureacompound   8.0 agent Base oil (b) Synthetic ester oil *¹ — 17.4  17.2 17.2  (mixing (20) (20) (20) ratio %) (c) -1 Mineral oil 51.0  52.2 51.6  51.6  (60) (60) (60) (60) (c) -2 Synthetic 34.0  17.4  17.2  17.2 hydrocarbon oil *² (40) (20) (20) (20) Additives (d) Molybdenum 2.0 —2.0 2.0 dialkyldithiocarbamate *³ (e)Molybdenum disulfide *⁴ 3.0 3.0 3.03.0 (f) Polytetrafluoroethylene *⁵ 1.0 1.0 — 1.0 (g) Zincdithiophosphate 1.0 1.0 1.0 — compound *⁶ Worked penetration 300Evaluation of variation in rotating x x x x torque at −40° C. *¹ Esteroil: Trimellitic acid-trialkyl ester having a flow point of −50° C. anda kinetic viscosity of 53 mm²/s at 40° C. *² Synthetic hydrocarbon oil:Polyalphaolefin oil having a kinetic viscosity of 420 mm²/s at 40° C. *³Molybdenum dialkyldithiocarbamate: (R³R⁴N—CS—S)₂—Mo₂O_(m)S_(n) whereinR³ and R⁴ represent C₁-C₄ alkyl groups, m is 0-3, n is 1-4 and m + n =4. *⁴ Molybdenum disulfide (average particle size, 0.45 μm) *⁵Polytetrafluoroethylene (average particle size, 0.2 μm) *⁶ Zincdithiophosphate compound: Zinc dialkyldithiophosphateTest for Variation in Rotational Torque

A constant velocity joint was left alone under an atmospheric conditionat −40° C., and variation range of the torque at the output axis wasmeasured when starting to rotate with θ=40 deg. Evaluation was conductedusing a fixed type constant velocity joint in the present test. Thevariation range at the output axis was assessed according to thefollowing criterion for average torque.

o: cleared (less than 20% variation range)

x: failed (not less than 20% variation range)

Results

The grease compositions for a constant velocity joint according to thepresent invention in Examples 1-4 show excellent potentials in reducingvariations in rotational resistance at a low temperature in comparisonto those in comparative examples 1-4 which do not contain component (b),(d), (f) or (g).

What is claimed is:
 1. A grease composition for a constant velocityjoint, said composition comprising a base oil, a thickening agent andadditives, wherein: said thickening agent consists of (a) a diureathickening agent which is a reaction product ofdiphenylmethane-4,4′-diisocyanate with octylamine and octadecylamine,said base oil consists of (b) a trimellitic acid-trialkyl ester oil and,(c) a mineral oil and/or a polyalphaolefin oil, and said additivescomprise the following components (d) to (g): (d) a molybdenumdialkyldithiocarbamate of the following formula:(R³R⁴N—CS—S)₂—Mo₂O_(m)S_(n) wherein R³ and R⁴ represent C₁-C₄ alkylgroups, m is 0-3, n is 1-4 and m+n=4, (e) molybdenum disulfide, (f) apolytetrafluoroethylene, and (g) a zinc dithiophosphate compound,wherein a flow point of the component (b) is not higher than −40° C.,wherein a kinetic viscosity of the component (b) is not less than 40mm²/S at 40° C., wherein the content of the component (a) is 2-20% bymass and is sufficient to make worked penetration of the greasecomposition within a range of 250-350, the content of the component (b)is 8.5-34% by mass, the content of the component (c) is 40-80% by mass,the content of component (d) is 0.5-5% by mass, the content of thecomponent (e) is 0.5-5% by mass, the content of the component (f) is0.5-5% by mass and the content of the component (g) is 0.5-5% by massbased on the total mass of the composition, wherein the base oilconsists of 10 to 40% by mass of the component (b) and 90 to 60% by massof the component (c) based on the total mass of the base oil.
 2. Thegrease composition for a constant velocity joint according to claim 1,wherein the torque transmission part of the constant velocity joint isin the shape of a ball.
 3. The grease composition for a constantvelocity joint according to claim 1, wherein said constant velocityjoint is a fixed type constant velocity joint.
 4. The grease compositionfor a constant velocity joint according to claim 1, wherein saidconstant velocity joint is a sliding type constant velocity joint.
 5. Aconstant velocity joint which comprises the grease composition for aconstant velocity joint according to claim
 1. 6. The constant velocityjoint according to claim 5, wherein the torque transmission part of theconstant velocity joint is in the shape of a ball.
 7. The constantvelocity joint according to claim 5, wherein said constant velocityjoint is a fixed type constant velocity joint.
 8. The constant velocityjoint according to claim 5, wherein said constant velocity joint is asliding type constant velocity joint.